The present invention relates to cameras with xe2x80x9cthrough-the-lensxe2x80x9d lighting and in particular to cameras with xe2x80x9cthrough-the-lensxe2x80x9d lighting and a dual-modulation system for protecting the photosensitive surface from stray light.
In cameras, true frontal lighting is achieved when the light source is positioned behind the lens, on the lens""s optical axis. To reach the image, the light must pass through the lens. With xe2x80x9cthrough-the-lensxe2x80x9d lighting there is no shadowing.
The condition of no shadowing is valuable for general photography. It is also important in optical-ranging applications for distance measuring and for acquiring three-dimensional views. Theoretically, in optical-ranging applications, the distance between the camera and a point on a scene is directly related to the amount of reflected radiation from that point. Clearly shadowing introduces errors to the measurements.
An added advantage of xe2x80x9cthrough-the-lensxe2x80x9d lighting is that by proper arrangement, it is possible to illuminate substantially only the field of view of the camera. Thus, light losses are be minimized.
Naturally, positioning the light source behind the lens, on the optical axis, would block reflected radiation from the scene; a shadow of the light source would be formed on the photosensitive surface. However, the light source can be located behind the lens, sufficiently offset from the optical axis so as not to block the path of reflected radiation from the scene. The light is boresighted with the optical axis using a beamsplitter or a mirror.
Cameras with xe2x80x9cthrough-the-lensxe2x80x9d lighting, using a coherent, collimated, internal light source, are known. U.S. Pat. No. 5,200,793, which is incorporated herein by reference, describes an optical-ranging camera with xe2x80x9cthrough-the-lensxe2x80x9d lighting wherein the light passes through an expander/collimator, collimating the beam and modifying its diameter. It is then boresighted with the optical axis using a beamsplitter and directed through a objective lens; the desired field of view is illuminated. A light modulator on the optical axis modulates both outgoing light and reflected radiation from the scene, according to a wave function, generally a sinusoidal wave function. Generally, the light source is laser light. A band-pass filter, adjacent to the photosensitive surface, protects the photosensitive surface from ambient light. However, the band-pass filter does not protect the photosensitive surface from stray light originating from the internal light source (and having essentially the same frequency as reflected radiation from the scene).
It is an aspect of some preferred embodiments of the present invention that a camera be constructed with xe2x80x9cthrough-the-lensxe2x80x9d lighting, wherein a light source is located behind the lens. Preferably, the light is boresighted with the optical axis of the camera, using a beamsplitter or a mirror.
In some preferred embodiments of the present invention, a source of incoherent light is used. Alternatively, a source of coherent light is used.
In some preferred embodiments of the present invention, the light is collimated and the beam diameter modified such that the light that emerges through the lens illuminates substantially only the field of view of the camera.
In preferred embodiments of this aspect, FOV, the field of view of the camera is substantially equal to FOI, the field of illumination. As a result, shadowing is eliminated, illumination of the scene is homogenous and the sense of depth is improved, all these leading to optimal illumination.
Alternatively or additionally, an extended light source is preferably used, wherein the light is not collimated. Preferably the light source has an optical extent substantially the same as that of the photosensitive surface. This means that the effective angle illuminated by the light source as it leaves the camera (FOI) is the same as the effective angle viewed by photosensitive surface (FOV).
An aspect of some preferred embodiments of the present invention is that a camera with xe2x80x9cthrough-the-lensxe2x80x9d lighting include a variable-aperture iris, adjacent to the light source, in order to reduce the beam diameter, when desired, such that only a portion of the field of view is illuminated. In preferred embodiments of this aspect, partial illumination of the field of view is made possible. However, generally, the best mode operation is when FOV is substantially the same as FOI.
An aspect of some preferred embodiments of the present invention is that a camera with xe2x80x9cthrough-the-lensxe2x80x9d lighting include a dual modulation system comprising a fast light modulator positioned between the beamsplitter (or mirror) and the photosensitive surface and a fast light modulator positioned between the beamsplitter (or mirror) and the light source. A controller, or some appropriate circuitry, controls the two modulators and the light-source. Alternatively, the photosensitive surface itself is switched between an on and off so that it does or does not react to the light incident on it.
In some preferred embodiments of this aspect, a method of dual modulation is carried out which substantially blocks light from reaching the photosensitive surface (or turns the surface off) whenever the light-source is on, yet insures that all the desired radiation reflected from the scene is collected.
Alternatively or additionally, a method of dual modulation is carried out as an effective gain control, to equalize, to some extent, the amount of light reflected from the main object and the amount of light reflected from the background. This serves to increase the signal to noise ratio of a resultant image while avoiding overloading of those portions of the photosensitive surface that image bright parts of the image.
An aspect of some preferred embodiments of the present invention is that a camera with xe2x80x9cthrough-the-lensxe2x80x9d lighting be constructed in the CMOS technology, with only one fast light modulator, positioned between the beamsplitter (or mirror) and the light source. Modulation of the photosensitive area is carried out at the level of the pixels. A controller, or some appropriate circuitry, controls the modulation of the light-source and the modulation of the pixels.
In preferred embodiments of this aspect, a program of dual modulation is carried out which substantially blocks light from activating the photosensitive surface whenever the light-source is on. Since gating of the photosensitive area is carried out at the level of the pixels, it is possible to control the amount of radiation reflected from the scene that is collected on each pixel. In this manner, effective gain control, equalizing the amount of light reflected from the main object and the amount of light reflected from the background is better achieved.
There is thus provided, in accordance with a preferred embodiment of the invention, a camera with through-the-lens lighting, comprising:
a light source that produces incoherent light;
a photosensitive surface;
focusing optics, having an optical axis, that forms an image of a scene, within a field of view, on the photosensitive surface,
wherein the light is boresighted with the optical axis and directed toward the scene, illuminating substantially only the field of view of the camera.
Preferably, the focusing optics comprises telecentric optics which collimates reflected radiation from the scene.
Preferably, the focusing optics includes a collimating lens which collimates the light.
In a preferred embodiment of the invention, the camera is an optical ranging camera and comprising a single modulator which modulates both the collimated, incoherent light and reflected radiation from the scene, wherein only a desired, gated portion of the reflected radiation from the scene is collected and wherein intensity values of the image are indicative of distances of objects from the camera.
Preferably, the light source is a modulated light source and the light reaching the photosensitive surface is modulated by a modulator.
Preferably, the light source is modulated and the sensitivity of the photosensitive surface is modulated.
There is further provided, in accordance with a preferred embodiment of the invention, a camera with through-the-lens lighting, comprising:
a modulated light source;
a photosensitive surface;
focusing optics, having an optical axis, that forms an image of a scene, within a field of view, on the photosensitive surface, wherein the light is boresighted with the optical axis and directed toward the scene, illuminating substantially only the field of view of the camera;
a modulator which modulates radiation striking the photosensitive surface or the sensitivity of the photosensitive surface, wherein the modulator does not modulate the light source; and
a controller, controlling the modulator and the modulation of the light-source, to block a reaction of the photosensitive surface whenever the modulated source of light is on, while insuring that all the desired radiation reflected from the scene is collected.
Preferably the camera includes a collimating lens which collimates the light.
In a preferred embodiment of the invention, the light is coherent. Alternatively, the light is incoherent.
In a preferred embodiment of the invention, the camera is an optical ranging camera, only a desired, gated portion of the reflected radiation from the scene is collected and intensity values of the image are indicative of distances of objects from the camera.
In a preferred embodiment of the invention, the focusing optics comprises telecentric optics which collimates also reflected radiation from the scene.
In a preferred embodiment of the invention the modulator is operative to vary the sensitivity of the photosensitive surface.
In a preferred embodiment of the invention, the modulator modulates radiation striking the photosensitive surface and transmits substantially all the reflected radiation from the scene that reaches the camera.
In a preferred embodiment of the invention, the camera includes:
a controller, controlling the modulator and the modulation of the light-source, to block activation of the photosensitive surface whenever the modulated source of light is on, while insuring that all the desired radiation reflected from the scene is collected.
In a preferred embodiment of the invention, the modulator does not modulate the light from the light source that illuminates the scene.
Preferably, the controller provides a plurality of light pulses such that a total desired amount of light reaches the photosensitive surface from the scene.
In a preferred embodiment of the invention, the source and photosensitive surface have substantially equivalent optical extents, so that light emerges through the lens, illuminating substantially only the field of view of the camera.
In a preferred embodiment of the invention, the light source is an extended light source and comprising a variable-aperture iris adjacent to the extended source for controlling the extent of the illuminated field of view.
There is further provided, in accordance with a preferred embodiment of the invention, a method of creating an image with through-the-lens lighting comprising:
boresighting the beam with the optical axis of a camera, having a field of view; and
illuminating a scene with a beam of incoherent light, emerging from the camera along the optical axis, such that only the field of view of the camera is illuminated by the beam.
There is further provided, in accordance with a preferred embodiment of the invention, a method of creating an image with through-the-lens lighting comprising:
providing a modulated beam of light;
boresighting the beam with an optical axis of a camera having a field of view;
illuminating a scene with the beam, emerging from the camera, such that substantially only the field of view of the camera is illuminated; and
modulating the activation of a photosensitive surface of the camera in synchrony with the beam modulation, such that light is blocked from activating the photosensitive surface whenever the beam is on, while insuring that all the desired reflected radiation from the scene is collected on the photosensitive surface.
Preferably, modulating the activation comprises blocking light from incidence on the photosensitive surface.
Preferably, modulating the activation comprises modulating the sensitivity of the photosensitive surface.
Preferably, the method includes collimating the beam.
There is further provided, in accordance with a preferred embodiment of the invention, a method of creating an image with through-the-lens lighting comprising:
providing a beam of light, emanating from an extended source, internal to a camera;
boresighting the beam with an optical axis of the camera; and
illuminating a scene with the beam, emerging from the camera, such that substantially only a field of view of the camera is illuminated.
Preferably, the method includes:
modulating the beam; and
modulating the activity of the photosensitive surface in synchrony with the beam modulation, blocking light from activating the photosensitive surface whenever the beam is on, while insuring that all the desired reflected radiation from the scene is collected.
In a preferred embodiment of the invention, modulating the activity comprises blocking light from reaching the photosensitive surface. Alternatively, modulating the activity comprises modulating the sensitivity of the photosensitive surface.
In a preferred embodiment of the invention, modulating activation of the photosensitive surface in synchrony with the beam comprises:
estimating the average distance to the scene and the depth of scene;
modulating the light source with a multiple-pulse function of square pulses having a duration of xcex41 seconds each, xcex42 seconds apart, wherein during xcex41, light is transmitted and during xcex42, light is blocked; and
modulating activation of the photosensitive surface with a multiple-pulse function of square pulses that is included within the inverse of the light-source modulation function, so that during xcex41, the surface is not sensitive to light and during at least part of xcex42, the surface is sensitive to light.
In a preferred embodiment of the invention, the duration of the light pulse, is shorter than twice the time taken for light to propagate to the scene and wherein xcex41+xcex42, the time for a complete modulation cycle, is greater than the total time for light to propagate to the scene and for reflected radiation from all points on the scene to be recovered.
In a preferred embodiment of the invention, estimating comprises:
focusing the camera on the scene using the camera""s focusing optics;
determining the distance to a point of optimum focus based on the setting of the focusing optics;
determining the depth of field of the focusing optics for that setting;
estimating the distance to scene based on the distance to a point of optimum focus; and
estimating the depth of the scene based on the depth of field of the focusing optics for that setting.
In a preferred embodiment of the invention, estimating comprises:
setting the camera to a range-determining mode;
varying the modulation function; and
using the first few images to estimate the distance to the scene and the depth of the scene.
Preferably, a number of pulses of light illuminates the scene to provide a desired illumination thereof, said desired illumination being based at least in part on the determined distance.
In a preferred embodiment of the invention, estimating comprises setting the value of distance to the scene plus the depth of the scene to be equal to the range of the light source.
In a preferred embodiment of the invention, modulating activation of the photosensitive surface in synchrony with the beam comprises:
estimating the amount of light reflected from different portions of the scene which reaches the camera from various parts of the scene; and
modulating the light source, responsive to said estimate, with a multiple-pulse function of square pulses having a duration of xcex41 seconds each, xcex42 seconds apart, wherein during xcex41, light is transmitted and during xcex42, light is blocked; and
modulating activation of the photosensitive surface with a multiple-pulse function of square pulses that is included within the inverse of the light-source modulation function, so that during xcex41, the surface is not sensitive to light and during at least part of xcex42, the surface is sensitive to light, so as to adjust the range of light reaching various portions of the photosensitive surface.